Electronic assembly

ABSTRACT

An electronic assembly includes a first substrate and a second substrate, a hole through the first substrate, the second substrate having a trace with an indentation, an electronic device mounted over the indentation in the trace, and the first substrate is attached to the second substrate such that the electronic device is positioned within the hole through the first substrate.

This patent application is a continuation of U.S. patent applicationSer. No. 12/764,069 filed Apr. 20, 2010.

Light emitting devices may emit light through multiple surfaces. In anassembled product, it is common to provide a reflecting cup to redirectlight emitting from some surfaces toward a desired primary direction. Itis also common to encapsulate the assembled product, and to form theencapsulation material into a lens to further direct the emitted light.The reflecting cup may, for example, be mechanically evacuated (forexample, drilled) from a solid substrate and the entire surface of thereflecting cup may be plated with a reflective material (for example,with gold or silver). The light emitting device may then be mounted ontothe plated cup by using an adhesive (for example, conductive silverepoxy or non-conductive clear epoxy or silicone).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-section side view illustrating an example embodimentof an electronic assembly.

FIG. 1B is a cross-section top plan view of the electronic assembly ofFIG. 1A.

FIG. 2A is a flow chart illustrating an example method of manufacturingan electronic assembly.

FIG. 2B is a continuation of the flow chart of FIG. 2A.

DETAILED DESCRIPTION

The inventors have discovered that a light emitting device may notadhere well to the smooth flat plating material on a reflecting cup, sothe assembly may be prone to de-lamination between the light emittingdevice and the plated reflecting cup. In addition, the encapsulationmaterial may not adhere well to the plating material of the reflectingcup, and the assembly may be prone to delamination between theencapsulation material and the plated reflecting cup. Typically, thelight emitting devices generate a substantial amount of heat, whichfurther stresses bonding between the various materials. Each of thesepotential de-lamination possibilities affects product reliability. Thereis an ongoing need to improve reliability.

FIG. 1A illustrates an example embodiment of an electronic assembly 100.In the illustrated assembly, there is a first substrate 102 and a secondsubstrate 104. The substrates may be printed circuit board material (forexample, FR4, or flexible printed circuit materials), or may be ceramicor other substrates suitable for electronic assemblies. The firstsubstrate 102 has a cone shaped hole (106), forming an opening on eachof two opposite sides of the first substrate. One opening is smallerthan the other. The two substrates are attached so the smaller openingin the first substrate 102 is adjacent to the second substrate 104. Thewalls (108) of the hole are coated or plated with a reflective material(for example, gold or silver). The second substrate 104 has at least oneconductive trace 110. A light emitting device 112 is attached to thetrace 110 (for example, by conductive silver epoxy or non-conductiveclear epoxy or silicone). The light emitting device 112 may beelectrically connected to the trace 110, for example, by using a wirebond 113. The light emitting device 112 may be, for example, asemiconductor die including a Light Emitting Diode (LED). The lightemitting device 112 may emit light from a top surface (as viewed in FIG.1A), or side surfaces, or both. The light may be emitted over a wideangle. Some light from the light emitting device 112 passes directlythrough the hole 106 in the first substrate 102, and some light from thelight emitting device 112 is reflected from the reflective walls 108 andthen through the hole 106. The assembly is encapsulated by a transparentencapsulate 114, which may be, for example, epoxy or silicone. Thesurface of encapsulate 114 may be shaped to form a lens to furtherdirect light from the light emitting device.

FIG. 1B illustrates a cross-section top plan view of the electronicassembly of FIG. 1A. The cross-section is along the top surface of trace110. A dashed-line circle 134 depicts the position of the smalleropening in the side of the first substrate 102 (the opening itself isnot visible in the plane of the cross-section of FIG. 1A). Trace 110includes an indentation 116. The shape of the indentation 116 isillustrated as a “plus sign” as an example of a shape of an indentation,but the actual shape is not important. The indentation 116 may be filledwith an adhesive, and the light emitting device may be mounted over theindentation 116. The indentation may be an opening completely throughthe trace, so that the light emitting device is directly attached to thesecond substrate 104 in addition to being attached to the trace 110.Alternatively, the indentation may not be completely through the trace.The indentation provides an irregular three-dimensional surface (notflat) including side walls for improved adhesion. It is not necessaryfor the indentation 116 in the trace 110 to be completely enclosed bythe trace 110. The indentation 116 just needs to provide an irregularshape for adhesion. In addition, the indentation may only partiallyexpose the second substrate 104 so that the light emitting device 112 isdirectly attached to the second substrate 104 in addition to beingattached to the trace 110. Attaching the light emitting device 112 to anirregular shape of an indentation, and/or directly to the surface of thesecond substrate 104, provides a more robust attachment (relative toattaching to a smooth flat metal surface), which reduces the likelihoodof de-lamination.

In contrast to the prior art, the entire reflective cup in FIGS. 1A and1B is not plated with a reflective material, so that at least a portionof the surface of the second substrate 104 may be exposed to theencapsulate 114. Allowing the encapsulate 114 to directly bond to thesurface of the second substrate 104 provides a more robust attachment,which reduces the likelihood of de-lamination.

As an alternative to the encapsulate 114 directly bonding to the surfaceof the second substrate 104, the area surrounding the light emittingdevice 112 on the second substrate 104 may be printed or coated with awhite or other light-colored high-temperature ink or solder mask toprovide better reflectivity. Adhesion between the encapsulate and asubstrate coated with ink or solder mask is still more robust thanadhesion between an encapsulate and a smooth flat metal ‘plating.

In FIG. 1A, the first substrate 102 may be attached to the secondsubstrate 104 by using a bonding film 118. The bonding film 118 may be,for example, Prepreg (for example, R04400 Prepreg from RogersCorporation, 100 S. Roosevelt Ave., Chandler, Ariz. 85226). The bondingfilm 118 may have a hole formed (for example, drilled, punched, oretched) before lamination, so that the hole in the film (depicted inFIG. 1B by a dashed-line circle 136) is slightly larger than the smalleropening of the hole 106 in the first substrate 102 (depicted in FIG. 1Bby dashed-line circle 134). The resulting laminated structure will thenhave a recessed area 120, forming a gap between the first substrate 102and the second substrate 104 around the opening in the bonding film 118.The encapsulate 114 may at least partially extend into the gap, creatingan anchoring lock for the encapsulate, further preventing de-lamination.

In FIG. 1A, there may be a second trace 122 on the second substrate 104,and the light emitting device 112 may be electrically connected to thesecond trace 122 by a bonding wire, depicted by dashed line 124 in FIG.1A. Alternatively, the first substrate 102 may have a trace 126, and thelight emitting device 112 may be electrically connected to trace 126 bya bonding wire, depicted by dashed line 128 in FIG. 1A. The assembly 100may be electrically connected to another assembly by, for example,solder pads 130. Traces 122 or 126, and trace 110, may be electricallyconnected to solder pads 130 by metal plating 132. Alternatively, traces122 or 126, and trace 110, may be electrically connected to solder pads130 by plated through-holes or vias, depicted by dashed lines 134 inFIG. 1A.

The indentation 116 in the trace 110 may have a metal bottom surfaceinstead of an opening completely through the trace 110. For example,within the indentation 116, the second substrate 104 may be lightlyplated (plated but not filling the indentation 116 to the top of thetrace). Alternatively, the indentation 116 may be partially etchedwithout etching all the way through the trace 110. For light emittingdevices that generate a substantial amount of heat, a metal bottomsurface in the indentation helps dissipate heat, perhaps at the expenseof some adhesion, but adhesion to the irregular shape and walls of theindentation is better than adhesion to a smooth flat metalized surface.

The assembly 100 illustrated in FIGS. 1A and 1B may be a packagecomprising a single light emitting device. Alternatively, the assembly100 may be one element of a larger assembly having a plurality of lightemitting assemblies, or one element of an array of light emittingassemblies.

FIG. 2A illustrates an example method of making an electronic assemblyas depicted in FIGS. 1A and 1B. Note, the order of the steps asillustrated in FIGS. 2A and 2B does not imply a required order, and somesteps may be performed simultaneously or may be performed in othersequences. In addition, not all of the illustrated steps are required,and in particular, the designation of a step as optional or alternativedoes not imply that steps not so designated are required. At step 200, ahole is fabricated through two sides of a first substrate (for example,by drilling), where an opening in one side is smaller than the openingin the other side. At alternative step 202, a bonding film is fabricatedwith an opening that is larger than the smaller opening in the firstsubstrate. At step 204, a trace is fabricated on a second substrate, thetrace having an indentation (or opening). At step 206, the twosubstrates are attached so that the indentation in the trace is withinthe smaller opening on the first substrate. In FIG. 2B, at alternativestep 208, the two substrates are attached using the bonding film betweenthe two substrates, with the opening in the bonding film forming a gapbetween the two substrates. At step 210, a light emitting device isattached to the trace over the indentation in the trace. At step 212,the assembly is encapsulated such that at least some encapsulatedirectly bonds with the second substrate, or to an ink or solder resiston the second substrate. At alternative step 214, encapsulation resultsin at least some encapsulate within the gap formed by the opening in thebonding film.

As discussed above, the disclosed light emitting device assemblyprovides at least three improvements to decrease de-lamination: (1)attaching the light emitting device to an irregular surface such as anindentation (or opening) in a trace, and/or attaching the light emittingdevice directly to the second substrate; (2) bonding the encapsulatedirectly to the second substrate (or to a substrate coated with an inkor solder mask); and (3) providing a recessed anchoring lock (gapbetween substrates) for the encapsulate. The improvements may beimplemented individually, or in any combination.

1. An electronic assembly, comprising: a first substrate having a hole;a second substrate, the first substrate attached to the secondsubstrate; a first trace on the second substrate, the first trace havingan indentation completely enclosed by the first trace; a light emittingdevice attached to the first trace at the indentation in the firsttrace; and, the light emitting device positioned within the hole in thefirst substrate.
 2. The electronic assembly of claim 1, the indentationcomprising an opening through the first trace, the light emitting deviceattached to the second substrate through the opening in the first trace.3. The electronic assembly of claim 1, further comprising a second traceon the second substrate, the light emitting device electricallyconnected to the second trace.
 4. The electronic assembly of claim 1,further comprising a second trace on the first substrate, the lightemitting device electrically connected to the second trace on the firstsubstrate.
 5. The electronic assembly of claim 1, the light emittingdevice comprising a Light Emitting Diode.
 6. The electronic assembly ofclaim 1, further comprising an encapsulate, the encapsulate directlybonded to at least a portion of the second substrate.
 7. The electronicassembly of claim 1, further comprising: the first substrate having areflective coating; and, an encapsulate, the encapsulate bonded to thereflective coating.
 8. The electronic assembly of claim 1, furthercomprising: a bonding film between the first and second substrates, thebonding film having an opening that is larger than the hole in the firstsubstrate, the bonding film positioned so that a gap is formed betweenthe first and second substrates within the opening in the bonding film;and, an encapsulate, the encapsulate at least partially within the gap.9. An electronic assembly, comprising: a first substrate, a hole throughthe first substrate; a second substrate; a first trace on the secondsubstrate, the first trace having an indentation completely enclosed bythe first trace; a bonding film between the first and second substrates,the bonding film having an opening, the bonding film positioned so a gapis formed between the first and second substrates within the opening inthe bonding film; an electronic device mounted on the second substratewithin the hole though the first substrate and attached to theindentation with an adhesive; and, an encapsulate, encapsulating theelectronic device, the encapsulate at least partially extending into thegap between the first and second substrates.
 10. The electronic assemblyof claim 9, further comprising a second trace on the second substrate,the light emitting device electrically connected to the second trace.11. The electronic assembly of claim 9, further comprising a secondtrace on the first substrate, the light emitting device electricallyconnected to the second trace on the first substrate.
 12. The electronicassembly of claim 9, the light emitting device comprising a LightEmitting Diode.
 13. The electronic assembly of claim 9, furthercomprising an encapsulate, the encapsulate directly bonded to at least aportion of the second substrate.
 14. The electronic assembly of claim 9,further comprising: the second substrate having a reflective coating;and, an encapsulate, the encapsulate bonded to the reflective coating.15. The electronic assembly of claim 9, further comprising: a bondingfilm between the first and second substrates, the bonding film having anopening that is larger than the hole in the first substrate, the bondingfilm positioned so that a gap is formed between the first and secondsubstrates around the opening in the bonding film; and, an encapsulate,the encapsulate at least partially within the gap.
 16. A method ofmaking an electronic assembly, comprising: fabricating a hole throughtwo sides of a first substrate, a first the opening of the hole in oneside is smaller than a second opening of the hole in the other side;fabricating a first trace on a second substrate, the first trace havingan indentation completely enclosed by the first trace; attaching thefirst and second substrates so that the indentation in the first traceis within the smaller opening on the first substrate; and, attaching anelectronic device to the indentation in the first trace.
 17. The methodof claim 16, further comprising: fabricating a bonding film with a thirdopening that is larger than the first opening of the first substrate;and, attaching the first and second substrates using the bonding filmbetween the two substrates, with the electronic device within the thirdopening in the bonding film, and with the third opening in the bondingfilm forming a gap between the first and second substrates within thethird opening in the bonding film.
 18. The method of claim 17, furthercomprising encapsulating the electronic assembly so that at least someof the encapsulate is within the gap.
 19. The method of claim 16,further comprising: encapsulating the electronic assembly so that theencapsulate directly bonds with at least a portion of the secondsubstrate.
 20. The method of claim 16, further comprising: coating atleast a portion of the first substrate with a reflective coating; and,encapsulating the electronic assembly so that the encapsulate bonds withthe reflective coating on the first substrate.